Some polymer-framed semi-autos that use the frame for guide/slide rails (like the Ruger P95) may need some time to wear-in, before they'll reliably cycle light loads.
Other than that... there isn't really anything to worry about.
And barrel break in? No. I don't bother.
I might clean the barrel after 20 to 50 rounds for a centerfire (rifle or handgun).
But, after that... it doesn't get any special treatment.
"Such is the strange way that man works -- first he virtually destroys a species and then does everything in his power to restore it."